The Color of Toast

From ColorWiki

This article has seen a lot of seminars. It is the simplest method I have found so far to introduce the concept of color management with a minimum of technical terms and concepts. I have had such good success with this analogy that I felt I should publish it here.

– Steve Upton

The Color of Toast

A lot has been written and said about color management in an attempt to describe what it is, what it solves and how it works. Like any discussion about computing, these descriptions often use fancy new terms that effectively confuse and turn off people who just want to understand, well, what it is, what it solves and how it works.

An effective and greatly simplified analogy is that of the toaster. Pay attention here because this is one even your clients will understand.
Let's say you get up in the morning, walk out to your kitchen and place a piece of bread in your toaster setting it to a level of "4". After a little while, a certain color of toast pops out - hopefully a pleasing color. Now if you take the next piece of bread in the loaf over to your neighbor’s and put it in his toaster at the same setting of "4" do you think you will get the same color of toast?

Probably not.

This is the problem of color management. The settings used on the toaster do not necessarily produce the same colors. As in the toaster, RGB and CMYK values on your computer are also just settings. And, just like the toasters, when they are sent to different devices, they produce different colors!

Now if you were a severe toast geek, you would toast 10 pieces of bread in your toaster; one at every setting. Then you would lay them all out in order on your kitchen table, grab the bag of bread and head over to your neighbor's. Avoiding his bewildered stares you would toast 10 pieces of bread in his toaster and take them back to lie on your table beside your toaster's work. Fanning through your ToasttoneTM independent toast guide* you would decide that "B" was, in fact, the color of toast you prefer. Looking up and down your toaster column you would confirm that yes, indeed, "4" is the setting on your toaster that will get you the color you want - you know this after several mornings of frantically waving smoke away from the alarm on your kitchen ceiling. After looking over your neighbor's toaster column, you note that a setting of "6" is what is needed to get the color you want from his toaster.

This, in essence, is what color management is all about: Carefully sampling what a device (monitor, printer, toaster, whatever) will do and then comparing it to an independent guide for actual color. In the case of the toast we used the fictitious Toast Guide and in the case of computers we typically use the Lab color space. Lab is a whole 3D range of numbers across 3 coordinates (L for lightness and a & b for color information). The important thing about Lab is that it is actually COLOR. That is, a number that represents a human sensation.

Let's take a little reminder on color. Color is a sensation produced by the cooperation of our eyes and our brains in response to mixtures of light. To have color you need

light,

an object and

an observer - for our purposes, a human observer.

Without all these components you do not have color.
Lab, as mentioned, is a whole range of numbers that are assigned to actual sensations. Each Lab number - like 50, 23, 47 - describes what a certain sample will look like under 5000K lighting (a graphic arts viewing standard in use in most viewing booths) and from a standard distance (creating a specifically sized spot on the retina) to an "average" person. In 1931 a group of scientists sat many people down to perform painstaking color tests to come up with this "average" person and for our purposes it works quite well.

Back to the toaster:

To get the same color from different toasters, we needed to sample all the colors of toast the lowly machine could produce and then compare them to an independent guide. This lookup table is the equivalent of an ICC profile.

To get the same color from different devices – the basis of what we are trying to do here - we need to sample all the colors each device can produce and create a table that converts between the device settings - say, monitor RGB - and the colors it produces at those settings. For a monitor we attach a device to it and run software that walks through a list of settings,: red (255,0,0), yellow (255,255,0), green (0,255,0), and so forth. At each RGB value, the software takes a reading with the instrument and gets a Lab color back. After running through a long list that only a computer should have to suffer, a profile is built for that monitor.

If we want to get the same color from our printer as well, we need to build a profile for it as well. The same technique applies. We send a file out to the printer that contains a long list of settings - for example: cyan (100,0,0,0), blue (100,100,0,0), magenta (0,100,0,0), and so forth. We then read each patch on the paper with a device like the Eye-One that supplies Lab values for each corresponding set of CMYK settings that were sent. A few calculations and your computer produces a profile for your printer.

“Great”, you think, “but how do I use these things?” That depends on what you are trying to achieve.

A good example is when you want to get the file you print to match the one you see on screen. The file on screen is, by definition, in MonitorRGB and you need to convert it to PrinterCMYK. If you assign the monitor profile to the file, it will convert all those MonitorRGB settings which are unique to your monitor to Lab (remember the toaster). Lab, you will recall, is color - so we are out of the arbitrary world of settings that only work for your monitor and on to something much more useful.

Any profile can be applied to those Lab values to get the color you want. In this case, we want the color to go to your printer. When the printer profile is applied it formulates the correct CMYK settings for each color in your file. A good quality profile will do a great job of matching those colors within the abilities of the printer.

At first blush it may seem like a toaster is an over-simplification of color management but the analogy actually fits quite well. When you are in the process of untangling a complicated workflow, just remember; they are all different toasters. A good profile for each device, applied properly and color will flow through your shop predictably.